<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        body {
            margin: 0;
            padding: 0;
            font-family: Arial, sans-serif;
        }

        .grid-container {
            display: grid;
            grid-template-columns: repeat(12, 1fr);
            gap: 20px;
        }

        .header {
            grid-column: 1 / span 12;
            padding: 20px;
            background-color: #333;
            color: white;
        }

        .nav {
            grid-column: 1 / span 4;
            padding: 20px;
            background-color: #f2f2f2;
        }

        .content {
            grid-column: 5 / span 8;
            padding: 20px;
            background-color: #f9f9f9;
        }

        @media (max-width: 768px) {
            .grid-container {
                grid-template-columns: repeat(1, 1fr);
            }
        }
    </style>
</head>
<body>


<div class="grid-container">
    <header class="header">Заголовок</header>
    <nav class="nav">Навигация</nav>
    <div class="content">Содержимое</div>
</div>
</body>
</html>